The present application relates to the fabrication of metallization structures for semiconductor devices, and more particularly, to the fabrication of metallization structures with reduced contact resistance.
In semiconductor technologies, tungsten (W) is typically used as a middle-of-the-line (MOL) contact material because of its relatively low resistance, less stress, and electromigration properties. MOL contacts are typically formed within contact openings present in a dielectric material layer deposited on top of active semiconductor devices. The MOL contact may extend to surfaces of the contact areas of underlying semiconductor devices. Due to the high aspect ratio and small feature size of the contact openings, W is deposited by a chemical vapor deposition (CVD) process, which usually includes a tungsten hexafluoride (WF6) precursor. To prevent the diffusion of fluorine during W deposition, a relatively thick metal liner with a thickness greater than 2 nm is required.
As the dimensions of MOL contacts are scaled down, the currently used W metallization scheme cannot meet the resistance targets for future technology nodes. This high resistance for W-based MOL contacts is a result of the need for a thick metal liner and the poor gap filling property of W which results in formation of seams and voids in the MOL contacts. Therefore, a method for forming MOL contacts with reduced contact resistance remains needed.